A climate agreement struck Thursday among 191 countries would allow airlines to grow in the coming decades without also growing their impact on the climate.

The International Civil Aviation Organization has agreed to encourage airlines to purchase credits through global carbon markets to offset their emissions for many flights beginning in 2021.

Those credits would balance pollution from jets and other commercial aircraft through conservation measures made elsewhere. Those measures could include renewable power projects, energy efficiency efforts or the substitution of coal-fired cookstoves with solar-powered cookers.

The plan would be phased in over the course of 14 years, beginning with the U.S. and other countries that have volunteered to require their airlines to obtain carbon offsets. Other member countries would follow between 2027 and 2035.

Earlier this year, the ICAO called for a 4 percent reduction in fuel consumption from new commercial aircraft built after 2028, and from those currently in production delivered after 2023.

Commercial airplanes are major emitters of the carbon dioxide contributing to climate change, accounting for 11 percent of all emissions from the global transportation sector. Those emissions are expected to grow by about 50 percent by mid-century as the demand for air travel increases worldwide Thursday's deal was hailed by the airline industry, but received mixed reviews from climate and energy experts.

Bob Perciasepe, president of the Center for Climate and Energy Solutions, said that the agreement is a major step in global efforts to combat climate change, and a sign that the momentum behind the Paris Climate Agreement continues to build.

"The agreement provides a practical framework for harnessing market forces to limit the rapid growth in airline emissions," he said. "International aviation is among the fastest growing sources of greenhouse gases. Without new measures, emissions are expected to triple by 2050."

Dan Rutherford, aviation program director for the International Council on Clean Transportation, said the deal doesn't sufficiently address the urgency of cutting carbon emissions from the airline industry.

"In the long run airlines need to decarbonize, not to pay others to do it for them," he said in a statement. "A host of new technologies to reduce aircraft emissions are under development today but need policy support. Since ICAO won't provide that, other measures will be needed."